1. Field of the Invention
The present invention relates to an ultrasonic diagnostic apparatus for transmitting ultrasonic waves to an object to be inspected, receiving ultrasonic echoes reflected from the object and displaying images on the basis of the received ultrasonic echoes. Further, the present invention also relates to a method of checking the performance of such an ultrasonic diagnostic apparatus.
2. Description of a Related Art
The quality of images displayed on an image display unit (for example, CRT, LCD, etc.) of an ultrasonic diagnostic apparatus deteriorates due to various factors. For example, a signal-to-noise ratio of images degrades with the deterioration of an ultrasonic transducer for transmission or reception of ultrasonic echoes, and the quality of the images also degrades with the deterioration of the image display unit.
When such image quality deterioration occurred in a conventional ultrasonic diagnostic apparatus, it was impossible to find out which caused the deterioration, the image display unit or another part inside the ultrasonic diagnostic apparatus, because the condition inside the ultrasonic diagnostic apparatus could not be checked. In that case, it was also impossible to analyze the image quality deterioration quantitatively.
In Japanese Patent Laid-open Publication JP-A-9-190170 (hereinafter referred to also as Reference 1), the applicant discloses an image display method in which image signals are subjected to gradation transformation processing based on predetermined gradation transformation conditions and then displayed on light-emitting display means, the method comprising the steps of detecting the external light level irradiated on the light-emitting display means and changing the gradation transformation conditions so as to obtain a desired gradation on the basis of the detection results. The image display method disclosed in Reference 1, however, can not quantitatively check the image quality deterioration due to various reasons, although it can change the gradation of displayed images as a function of the external light level.
In Japanese Patent Laid-open Publication JP-A-9-146513 (hereinafter referred to also as Reference 2), the applicant discloses an image display method in which image signals are subjected to gradation transformation processing and then displayed on light-emitting display means, the method comprising the steps of detecting the amount of deterioration in brightness of the light-emitting display means and correcting the brightness deterioration of the light-emitting display means on the basis of the detected amount of deterioration.
In Japanese Patent Laid-open Publication JP-A-9-212144 (hereinafter referred to also as Reference 3), the applicant discloses an image display method in which image signals are subjected to gradation transformation processing based on a predetermined gradation transformation table and then displayed on image display means, the method comprising steps of detecting the amount of deterioration of brightness of the image display means and correcting the gradation transformation table on the basis of the detected amount of deterioration so that the brightness deterioration of the image display means can be corrected.
The image display methods disclosed in References 2 and 3, however, can not quantitatively check the image quality deterioration due to various reasons, although they can correct brightness deterioration of the light-emitting display means or image display means.
In Japanese Patent Laid-open Publication JP-A-2000-278721 (hereinafter referred to also as Reference 4), the applicant discloses an image quality checking method for display units, the method comprising the steps of displaying specified test patterns on the screen of a display unit, storing the test patterns as digital data, comparing the stored digital data with reference data previously acquired in the same manner in that display unit and outputting a difference value between both data. The image quality checking method for display units disclosed in Reference 4, however, is not designed to evaluate the image quality affected by any part other than the image display unit of a medical diagnostic apparatus having a display unit, although it can quantitatively and objectively evaluate the quality of images appearing on the display unit.
In Japanese Patent Laid-open Publication JP-A-2000-287227 (hereinafter referred to also as Reference 5), the applicant discloses a sharpness measuring method for display units, the method comprising the steps of displaying rectangular wave test patterns including a plurality of line pairs corresponding to a plurality of frequencies at a fixed position on the screen of a display unit, storing the test patterns as digital data, finding the response corresponding to each frequency from the stored digital data, finding the CTF (contrast transfer function) value of the display unit from the response, and then calculating the MTF (modulation transfer function) value from the CTF value. The sharpness measuring method for display units disclosed in Reference 5, however, is not designed to evaluate the image quality affected by any part other than the image display unit of a medical diagnostic apparatus having a display unit, although it can accurately measure the sharpness of images appearing on the display unit.